High speed photographic light circuit



Jan. 10, 1961 R. B. HARTMAN ll HIGH SPEED PHOTOGRAPHIC LIGHT CIRCUIT Filed April 30, 1958 7 BY a:

United States Patent HIGH SPEED PHOTOGRAPHIC LIGHT CIRCUIT Robert B. Hartman II, Bridgeport, Conn., assignor to Remington Arms Company, Inc., Bridgeport, Conn., a corporation of Delaware Filed Apr. 30, 1958, Ser. No. 732,070

3 Claims. (Cl. 315-241) This invention relates to the field of high speed electrical photoflash lamps. More particularly this invention involves a novel improved high speed trip circuit for a high speed photoflash lamp for use primarily in ballistics testing and measurements for firearms and ammunition.

It is an object of this invention to provide an improved high speed trip circuit for a high speed photoflash lamp which is simple and economical in construction, efliciently and reliable in operation.

It is another object of this invention to provide an improved photoflash system which has very rapidlyoperating trigger pulse and an extremely short firing time.

Other objects and advantages will appear from the following specifications and claims taken with the accompanying drawings in which:

The single figure is a diagrammatic view of circuits and apparatus arranged and constructed according to one embodiment of the invention.

Referring to the figure by characters of reference, the circuit includes a triode 10, connected as a cathode follower for low impedance output, the grid of which receives the positive pulse of input voltage to trigger the photoflash function. Connected to the cathode of triode is a high voltage diode 12 preferably a IE3 and a high voltage condenser 13 which are in turn connected to the grid of thyratron tube 14 which is preferably a hydrogen thyratron 4C35. The anode of thyraton 14 is connected to a positive high voltage source through ground resistor 18 and its cathode is connected both to ground condenser 20 and directly to a negative high voltage source. A flash tube 19, preferably a Mullard LDSZ, of the gasfilled type capable of producing an intense light when an electric discharge is passed between anode and cathode terminals, is connected across the high voltage leads HV(+) and HV() as indicated. A trigger or igniting electrode is provided to be energized to initiate the discharge. The igniting electrode of the flash tube is connected through condenser 16 to the plate or output of thyratron 14. Resistor 17 between the cathode of the flash tube and its trigger electrode prevents the flash tube from functioning by maintaining the trigger electrode at flash tube cathode potential until a trigger pulse is received through condenser 16 from thyratron 14. Resistor 15 is connected between the grid and cathode of thyratron 14 and in like manner prevents thyratron 14 from generating a pulse until it is triggered by triode 10 through diode 12 and condenser 13.

In operation when a high DC. voltage is applied across leads HV(+) and HV(), condenser 16 will charge up to the full high voltage value through resistors 17 and 18. In a similar manner, condenser 13 will charge up to the voltage difierence between the negative side of the high voltage supply and the cathode voltage of the cathode follower through resistor 15 and diode 12. When a positive voltage pulse is applied to the grid of triode 10 the similar power pulse appears on the cathode of this 'is transmitted to the grid of thyratron 14 through diode 12 and condenser 13. This pulse is of such an amplitude to cause the thyratron 14 to fire, causing a very high voltage drop across resistors 17 and 18. Since the voltage across a condenser can not be changed instan taneously, the voltage change across resistor 17 is trans mitted through condenser 16 to the igniter electrode of the flash tube 19 causing the flash tube to conduct and emit the light pulse. Thyratron 14 may be considered as a short circuit on firing so that the junction of resistor 18 and condenser 16 changes from the positive high voltage potential HV(+) to the negative potential of the high voltage supply HV(-). Since the voltage across the condenser 16 may not change instantaneously, the junction of condenser 16 and resistor 17 which is directly connected to the ignition electrode of the flash tube 19, is driven below the negative high voltage value, i.e. becomes negative with respect to the adjacent electrode by the amount of the entire high voltage supply [HV(+)+HV(--)]. This in effect, in my preferred embodiment, applies a voltage differential of about 7500 volts between the igniter terminal and the negative electrode of flash tube 19 to initiate its flash action, when HV(+) is +3750 and HV() is -3750 volts.

The negative source of high voltage need not be grounded for this circuit to operate so long as condenser 13 and the series diode 12 can withstand the dilferential of voltage between the triode cathode and the negative value of the high voltage supply. In the case of a split high voltage supply where the voltage is half positive and half negative, on firing the flash tube 19, the negative source of high voltage is very rapidly returned toward ground value or to the de-ionizing potential of the flash tube due to the relatively high impedance of the high voltage supply. This obviously generates a high voltage pulse with respect to ground which will try to return to the triode through condenser 13. However, the pulse is in a positive-going" direction and is effectively blocked by the diode 12 in series with condenser 13. If the negative terminal of the high voltage supply is grounded, the diode may be eliminated.

The driving source impedance for the grid of the thyratron 14 must be low. Therefore a cathode follower arrangement with tube 10 was chosen to transfer this pulse. If the cathode of the thyratron 14 is grounded, the apparent source impedance will be as low as is necessary. However, if the negative terminal of the high voltage power supply is not directly grounded, it is essential that the low impedance path be provided for the triggering pulse for the thyratron 14. In the circuit shown, the complete load path on the cathode follower is through the diode 12, condenser 13, resistor 15 and condenser 20 to ground.

While I have fully described a preferred embodiment of my invention in accordance with the patent statutes,

modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of this invention as defined in the appended claims.

What is claimed is:

1. An electrical very high intensity short duration light flash producer system comprising in combination, a normally non-conducting high voltage luminescent-discharge lamp having a principal positive electrode and a principal negative electrode between which a discharge may pass when the lamp is conducting to produce light and an initiator electrode adjacent to said principal negative electrode and operative when energized to render the lamp conducting, means for connecting the principal electrodes to a high voltage power supply means to cause of very short duration, a first condenser and a second condenser, means for connecting the initiator electrode through said first condenser and a first resistor to the positive side of the power supply means, said second condenser connecting the negative side of said power supply to ground, means for connecting the initiator electrode to the negative side of the power-supplyrneans through asecond resistor, switching means connected in parallel across said first condenser and said second resistor for selectively connecting said first condenser to said negative side of said high voltage power source to cause said initiator electrode instantaneously to become a different potential with respect to said principal negative electrode and render said lamp conductingzto enable a discharge to pass between said principal electrodes and produce a very highintensity-fiash of light of extremely short duration.

2. A high speed high intensity light flash producer system comprising intcolmbination a source of supply of high-voltage tdirectcurrent, a flash lamp having an anode, a cathode and a control grid, means connecting said source to said anode and said cathode, a first resistor and a first condenser arranged in series and connected in parallel across said anode and said control grid, at second resistor connected in parallel across said control grid and said cathode, switch means in series with said first resistor responsive to a triggering voltage pulse to connect said condenser to said cathode to change instantaneously said cathode potential with respect to the potential of the control grid to cause the flash lamp to function, and a second condenser connected between ground and the negative side of said source of power.

3. The system of claim 2 in which said switch means comprises a normally non-conductive grid-controlled electric discharge device actuated by and coupled to means producing the triggering voltage pulse by a third condenser and a high voltage diode.

References Cited in the file of this patent UNITED STATES PATENTS Edgerton I an. 9, 1940 2,533,567 Erickson Dec. 12,1950

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